Functionalized SnO2 nanobelt field-effect transistor sensors for label-free detection of cardiac troponin

Real-time label-free electrical detection of proteins, including cardiac troponin (cTn), is demonstrated using functionalized SnO2 nanobelt field-effect transistors (FETs) with integrated microfluidics. Selective biomolecular functionalization of the active SnO2 nanobelt channel and effective passivation of the substrate surface were realized and verified through fluorescence microscopy. The validation/verification of the sensing scheme was initially demonstrated via detection of biotin–streptavidin binding: devices with single biotinylated SnO2 nanobelts showed pronounced conductance changes in response to streptavidin binding. Importantly, the pH-dependence of the conductance changes was fully consistent with the charged states of streptavidin at different pH. Moreover, the specificity of the sensors’ electrical responses was confirmed by co-labeling with quantum dots. Finally, the sensing platform was successfully applied for detection of the cardiac troponin I (cTnI) subunit within cTn, a clinically important protein marker for myocardial infarction.